Pace calculator

Find your running pace from a distance and time, or the time or distance from a pace. Includes splits and predicted race times.

By the Calcist team · Checked against known answers · Updated October 27, 2026

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How pace is calculated

pace = time ÷ distance
time = pace × distance
distance = time ÷ pace
speed = distance ÷ time
1 mile = 1.609344 km (exact)

Pace is the time for one kilometer or one mile. Speed is the reverse: distance per hour. A 6:00 per mile pace is 10 mph.

Race-time prediction (Riegel formula)

T₂ = T₁ × (D₂ ÷ D₁)^1.06

Peter Riegel found that, for runners, time grows a little faster than distance: doubling the distance takes about 2.08 times as long (2^1.06). The formula is an estimate. It works best between about 1 mile and the marathon, and assumes you've trained for the longer distance.

Worked example

You run 10 km in 50:00. Pace = 50 min ÷ 10 km = 5:00 per km. Per mile: 5:00 × 1.609344 = 8:02.8, shown as 8:03 per mile. Speed = 10 km ÷ (50/60) h = 12 km/h, or 7.46 mph.

Predicted marathon: 50:00 × (42.195 ÷ 10)^1.06 = 50:00 × 4.60 = about 3:50:01.

Race distances

Race	Kilometers	Miles
5K	5	3.107
10K	10	6.214
Half marathon	21.0975	13.109
Marathon	42.195	26.219

Limitations

Splits assume an even pace. Hills, wind, heat and fatigue change real splits.
Race predictions are less reliable from very short races, for beginners, and for ultramarathons.
GPS watches often measure a little long in races, so your watch pace may be slightly faster than the official one.

Sources

Riegel PS. Athletic records and human endurance. American Scientist. 1981;69(3):285–290 the paper behind the 1.06 exponent.

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

10 km in 50:00 is 5:00 per km ✓
10 km in 50:00 is 8:03 per mile ✓
Marathon in 3:30:00 is 8:01 per mile ✓
5 km at 6:00 per km takes 30:00 ✓
1 hour at 8:00 per mile covers 7.5 miles ✓
Riegel: 10 km in 50:00 predicts a 3:50:01 marathon ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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Questions people ask

How do I calculate my running pace?

Divide your time by your distance. 30 minutes for 5 km is 6:00 per km. To get pace per mile, multiply the per-km pace by 1.609344.

What pace do I need for a sub-4-hour marathon?

About 5:41 per km, or 9:09 per mile. Use Find pace with a marathon and 3:59:59 to see the exact splits.

How accurate is the Riegel race predictor?

It's a reasonable estimate for trained runners from about a mile to a marathon. It tends to be optimistic for the marathon if your weekly mileage is low.

How do I convert pace to speed?

Divide 60 by the pace in minutes. A pace of 8:00 per mile is 60 ÷ 8 = 7.5 mph.

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